I have a roughly 3 year old bantam cochin roo that became lethargic and thin. His head was dark blood red. Went off feed but was still drinking and had food and water in crop at time of death. food was from day before and not digested. I did not find any coccidia evidence in his cecum or intestines. his lungs appeared very small and deflated to me and I think that may have been something to do with it but I really don't know

this is what his head looked like but it was darker when alive. the stuff in his mouth was from the flies this morning laying eggs

there was watery green stool but I think that may have been from not digesting

this is what came out of the cecum and did not have a horrible odor like from coccidiosis

found something under his testicles along the backbone and I'm not sure if this is normal or maybe a tumor?

the mass in question cut open

lung

gizzard contents

one chick that died of coccidiosis (fast killing bloody kind)
you can see the blood in the cecum

as a non-expert, I think the mass you've found is part of the kidneys. In chickens, the kidneys are a multi-lobed organ that sit right up in the frame of the bird. However they shouldn't have all those white patches, which may be urates and would definitely be a sign of illness.

Infectious Bronchitis and Marek's can both cause white lesions in the kidneys, though with Marek's it's tumorous growths rather than urates.

Sorry about your bird, and I don't really know much about what may have gone wrong... Those are what I thought of looking at the photos.

the corn shouldnt be a problem, he had plenty of rocks to crush it up. I think i found the kidneys and they were ok at least i think that's what they were. I'm hoping someone with more experience can chime in